This invention relates to semiconductor lasers.
In some applications of semiconductor lasers it is desirable that the differential optical output power (or differential quantum efficiency) be as large as possible. If the differential quantum efficiency were unity, each additional electron flowing in the external circuit would achieve the ideal of generating precisely one additional lasing photon, which in a symmetric AlGaAs double heterostructure laser, for example, would correspond to a differential output power of nearly 0.8 mW/mA at each laser mirror. Although unity differential quantum efficiency has not been achieved, values as high as 0.78 have been measured and values in the range 0.2 to 0.6 are routine. It is conceivable that values more closely approaching unity will result from further device development efforts.
It is common, on the other hand, for some users of semiconductor lasers to prefer smaller rather than larger values of differential output power; for example, when feedback stabilized optical outputs are needed. Such lasers also burn out less easily when subjected to excessive current transients. It has also been observed that lasers with high differential quantum efficiencies tend more frequently to exhibit self-pulsations in certain current ranges.